To upgrade your Chapel, you need Ancient Dragon Eggs.
With each upgrade, you need more Ancient Dragon Eggs.
Below is a list of possible ways to gain these.
Gems
You can purchase Ancient Dragon Eggs using gems.
1 Ancient Dragon Egg = 15 Gems
10 Ancient Dragon Eggs = 125 Gems
100 Ancient Dragon Eggs = 1,154 Gems
1000 Ancient Dragon Eggs = 10,000 Gems
Campaign Elite Sweeps
You can sweet elite campaigns to pick up extra Ancient Dragon Eggs.
Elite 1-1
Elite 1-2
Elite 1-3
Elite 1-4
Elite 1-5
Elite 1-6
Chests
Chest from the VIP daily clan gifts (Kingsdor city) gives Ancient Dragon Eggs too.
VIP Daily Clan Gifts
You can collect 5 Ancient Dragon Eggs per gift from daily VIP Clan gifts (Once you have level 25 diplomacy for this city).
Regular Events
Every 3 hours, you can do a regular event (Have to complete 2 stages of it).
You gain 20 Ancient Dragon Eggs each time you complete it.